Maintenance of acid-base balance in man is largely dependent on the ability of the kidneys to reabsorb the bicarbonate present in the glomerular filtrate and to excrete the excess protons generated as end products of metabolism. In the distal tubule and collecting duct of the kidney urinary acidification is achieved by a process of active H+ transport into the urine. A wealth of information about the cellular mechanisms of urinary acidification by these segments of the kidney have been obtained by the use of a model epithelium, the turtle bladder. In this tissue H+ transport has been shown to be an active process that is tighly coupled to cellular metabolism. However, the details of the relationship between cellular metabolism and H+ transport remain largely unknown. Cellular metabolism clearly has a significant role in the regulation of urinary acidification, but the sites and mechanisms of this regulation have not been clearly defined. The broad objective of this proposal is to study the details of mechanisms which control urinary acidification in the turtle bladder. In order to do so I plan to use methods which allow the simultaneous meausrement of H+ transport, oxidative metabolism, and cellular energetics ((ATP), (ADP) and (Pi)) in the turtle urinary bladder to study the details of the relationship between transport and metabolism. This will be approached first by doing studies that identify the mechanisms which couple H+ transport to metabolism. Next, studies which detail the dependency of the normal components of the H+ transport pathway (i.e. active transport pathway, passive backleak pathway) on cellular energetics will be done. Studies are also planned which allow the use of cellular energetics to define the cell population responsible for H+ transport in the turtle bladder. Finally studies will be done which define the role of cellular metabolism in the modulation of H+ transport by extracellular factors such as aldosterone and serosal osmolatity. The information gained from the proposed studies will be of help in elucidating the cellular mechanisms of urinary acidification in the normal state as well as allowing one to identify the mechanism operant in some states of altered urinary acidification.